Short-term oxycodone exposure produces delayed and persistent gut microbiome disruption in mice

The gut microbiome is a critical part of host homeostasis, yet its resilience following opioid exposure remains poorly understood. While opioid-induced short-term dysbiosis is well documented, the long-term recovery dynamics following oxycodone remain unclear. This study characterized the temporal dynamics of the fecal microbiota in male C57BL/6J mice following a brief 3-day oxycodone regimen (5mg/kg, BID). 16S rRNA gene sequencing was performed at baseline, day 3, 10, 17, and 70. While acute post-treatment phases (day 3 to 10) showed subtle taxonomic shifts in Clostridium_sensu_stricto_1 and Romboutsia, significant community disruption emerged later. By day 17, beta diversity significantly differed from saline controls (P =0.002). At day 70, both alpha diversity (p=0.02) and beta diversity (P=0.007) remained significantly altered, characterized by enriched Akkermansia and Marvinbryantia alongside depleted Eubacterium_xylanophilum. These findings demonstrate that even brief oxycodone exposure triggers persistent, non-recovering dysbiosis that became detectable only after treatment cessation and persisted through day 70. This suggests that the window for microbiome recovery exceeds two months in mice (equivalent to several human years), highlighting a potential long-term risk for patients prescribed short-term opioid courses. ImportanceShort-term opioid exposure is generally assumed to cause only transient disruption of the gut microbiome. However, the duration of microbiome recovery following clinically relevant opioid treatment remains poorly defined. In this study, we show that a brief three-day course of oxycodone in mice resulted in delayed and persistent alterations in gut microbial community structure that remained detectable for at least 70 days after treatment cessation. Notably, significant divergence in microbial composition emerged weeks after exposure rather than immediately following treatment, suggesting that short-term opioid use may initiate longer-lasting remodeling of the gut microbiome than previously appreciated. These findings highlight the importance of considering extended recovery timelines when evaluating the microbiological consequences of opioid exposure.